1. Field of the Invention
The above invention relates, generally, to median barriers and, specifically, to an improved interlocking median barrier for use in highway systems.
2. Discussion of the Prior Art
Median barriers--generally relatively heavy concrete devices--are utilized for separating lanes of traffic from other lanes of traffic, construction work, etc. The barriers must be sufficiently heavy such that, if accidentally contacted by a moving vehicle, they will prevent the moving vehicle's from leaving its lane, thereby protecting construction workers or other lanes of traffic on the other side of the median barrier.
The widespread use of pre-cast reinforced concrete in median barriers is well known. However, as highway speeds have increased and as vehicle weight increases, the kinetic energy, which can be expended against a median barrier, has increased dramatically (the kinetic energy is linearly related to the weight of the vehicle but as the square of the vehicle's speed). There is an increasing need to insure that vehicles cannot pass through or substantially move a median barrier and thereby create a hazard to the adjacent lane of traffic or constructions workers or the like.
Median barriers have certain resistance to movement caused by the weight of the barrier and the coefficient of friction between the lower surface of the barrier and the roadway upon which the barrier is located. Because this coefficient of friction is generally fixed, the resistance to lateral movement is generally proportional to the weight of the barrier. For the convenience of construction crews, temporary barriers are on the order of 12 feet in length, although longer or shorter barriers could be provided if the need arose (if, for example, it were necessary to have barriers around a very sharp curve, shorter barriers would permit the outer edge of the curve to be lined with barriers without the barriers intruding on the roadway. Unfortunately, as a barrier becomes smaller, its weight is less and, thus, its resistance to lateral movement is less.
One answer to the problem of barriers being shifted under vehicle impact is to involve the weight and mass of adjacent barriers such that several adjacent barriers must be moved in the event of a vehicle impact thereby providing greater resistance to lateral movement. U.S. Pat. No. 4,059,362 issued to Smith on Nov. 22, 1977 illustrates a pre-cast reinforced concrete barrier with a vertical tongue-and-groove arrangement molded into the ends of the barrier. The tapered aspect of the tongue-and-groove arrangement allows a barrier to be placed adjacent another barrier with the tongue of one barrier engaged with the groove of another barrier thereby preventing lateral movement of one barrier with respect to the other.
In the event of a vehicle collision, the resistance to lateral movement is not only the resistance of that barrier which is struck but also, because of the tongue-and-groove arrangement, the lateral resistance of the adjacent barriers as well. A problem associated with these tongue-and-groove barriers is that only a small amount of lateral movement is necessary before the tongue-and-groove arrangement is out of alignment and the barrier involved in the collision is no longer restrained by adjacent barriers.
Attempts have been made to fix barriers together and/or pin them to the road surface to increase the lateral resistance to movement of roadway barriers. U.S. Pat. No. 4,681,302 issued to Thompson on Jul. 21, 1987 illustrates a loose hardware type barrier which has end fittings which align with the end fittings of adjacent barriers. A separate piece of hardware, a locking pin, is inserted and then driven into the roadway. While this permits secure interlocking of the barrier and the roadway, experience has shown that such interlocked loose hardware barriers are extremely difficult to replace and/or repair.
Even if the locking pin can be removed from the roadway surface and from the interlocking mechanism, because the remaining portion of the interlocking mechanism of one barrier is vertically interrelated with an adjacent barrier, the barrier cannot simply be raised out of place and a new barrier substituted. The barrier has to be slid sideways for some distance and then removed creating substantial difficulties in replacement. Furthermore and more importantly, in the event of an accident in which the barrier is struck with a large vehicle (in the case of a concrete truck or a semi-tractor trailer vehicle), the barrier may be badly broken with the interlocking pins of adjacent barriers bent under the impact. It will be impossible to remove the pins. This difficulty makes it extremely costly (in terms of time, expense and public inconvenience due to the time for replacement) in the event of an accident.
U.S. Pat. No. 5,464,306 issued to Cristiano on Nov. 7, 1995 is a suggested answer to the above barrier problems. A male protrusion built into the end of one barrier interlocks with a diagonal female protrusion on the end of another barrier so as to retain the barriers in an interlocked fashion in the event of a vehicle collision. However, should the barrier be damaged in the collision, it can readily be hoisted vertically and replaced with a similar barrier. However, there are some difficulties with the Cristiano system. Cristiano utilizes a hollow area in the bottom of the barrier and thus the female portion extends only from the top of the barrier to a lower portion of the barrier but not vertically over the complete height of the barrier. This tends to reduce the area of the interlocking structure thereby increasing the stress on the interlocking mechanism. Furthermore, the Cristiano interlocking mechanism, as seen in FIG. 5, comprises a diagonal tube in which one corner of the tube is removed. It can be seen that very little longitudinal stress would be necessary for the male portion 3 to effectively straighten out the outer two arms of the diagonal 9 and 12 under tensile forces. Accordingly, these deficiencies reduce the ability of a barrier under impact load to transmit the load to adjacent barriers and thereby use the lateral movement resistance of adjacent barriers to stabilize the barrier.
The Federal Highway administration, recognizing defects existing in current interlocked median barriers, published a research paper (Publication No. FHWA-TS-88-006) in which weaknesses of many concrete barrier connectors are disclosed (pages 7-8, 73-74). The FHWA study (page 69) indicated that "unanchored pins in pin and loop connectors have a tendency to `jump out` of loops during vehicle impact, thereby destroying the integrity of the connection." This study also discloses the weakness of dowel type and tongue-and-groove type connectors with respect to requiring movement and repositioning of adjoining barriers to free up a damaged unit so that a new unit can be installed.